Pyrroloquinoline quinone, the chemical name is 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, also known as methaxatin; it has the following structural formula:

Pyrroloquinoline quinone is a small molecule compound found in microorganisms, it is widely distributed in various tissues and organs of the human body and is called the fourteenth vitamin. It is widely used in the fields of medicines, functional foods and cosmetics. For example, pyrroloquinoline quinone can fully improve the body's immune function, in the field of medicines, pyrroloquinoline quinone can be used to prevent and cure liver damage, reduce damage of free radicals to the human body, conditioning a variety of nervous system diseases, promote the absorption of amino acids, promote the synthesis of growth factors, prevent and cure Alzheimer's disease, promote the synthesis of glutathione, and pyrroloquinoline quinone has a strong anti-cancer function. In addition, pyrroloquinoline quinone can be used as a health food with anti-aging effects in the field of foods; in the field of cosmetics, pyrroloquinoline quinone is an anti-allergic and skin-beautifying substance.
For polymorphic compounds, different crystal forms may have different physical and chemical properties; including melting point, chemical stability, apparent solubility, dissolution rate, optical and mechanical properties, etc. These physicochemical properties directly determine the effect of a specific crystal form in the fields of medicines, functional foods, cosmetics and the like. For example, the crystal form of the pyrroloquinoline quinone sodium salt obtained by the prior art method is unstable and has a high hygroscopicity and a large extent of variation of humidity within the temperature range of storage at normal temperature, and the solid state is not ideal and is not suitable for processing (filtering, drying, tabletting), thus adversely affecting the application and storage of the pyrroloquinoline quinone sodium salt. In the prior art, some modifications are made to the crystal form of pyrroloquinoline quinone sodium salt, for example, in the patent CN201080031945, the invention overcomes the defects of low crystallinity and high content of residual solvent reported in some literatures, but the prepared crystal form also has hygroscopicity, the crystal form A in CN201210452297.6 has improved hygroscopicity, the hygroscopicity is less than 3%, preferably less than 0.6% at 65%-85% RH, but such hygroscopicity still cannot satisfy the need of the preparation process that has high requirement on hygroscopicity of crystal forms.
Therefore, although some crystal forms of pyrroloquinoline quinone have been disclosed in the prior art (in addition to the two literatures that are mentioned above, the prior art includes but is not limited to the following literatures, JP 2005-530786 A, JP 2011-246442 A, JP 2007-269769 A, WO2011/007633, JPH07113024(B2), CN201280028888.9), there is still a need to develop a new crystal form that has better properties than the known crystal forms, and has broad application prospects. Compared with the prior art, the crystal form provided by the present invention has lower hygroscopicity and the hygroscopixity is less than 0.3%, preferably no hygroscopixity at 75% RH.
The present invention aims at providing a crystal form with high crystallinity, high product purity and low content of residual solvent, which is easy to be filtered, dried and stored, as well as providing an environment-friendly and pollution-free process.